BME280_math module¶
Since | Origin / Contributor | Maintainer | Source |
---|---|---|---|
2016-02-21 | vsky279 | vsky279 | bme280_math.c |
This module provides calculation routines for BME280/BMP280 temperature/air presssure/humidity sensors (Bosch Sensortec). Communication with the sensor is ensured by Lua code through I2C or SPI interface. Read registers are passed to the module to calculate measured values.
See bme280 Lua module for examples.
bme280_math.altitude()¶
For given air pressure (called QFE in aviation - see wiki QNH article) and sea level air pressure returns the altitude in meters, i.e. altimeter function.
Syntax¶
bme280_math.altitude([self], P, QNH)
Parameters¶
- (optional)
self
userdata or table structure so that the function can be directly called as object method, parameter is ignored in the calculation P
measured pressureQNH
current sea level pressure
Returns¶
altitude in meters of measurement point
bme280_math.dewpoint()¶
For given temperature and relative humidity returns the dew point in celsius.
Syntax¶
bme280_math.dewpoint([self], H, T)
Parameters¶
- (optional)
self
userdata or table structure so that the function can be directly called as object method, parameter is ignored in the calculation H
relative humidity in percent (100 means 100%)T
temperate in celsius
Returns¶
dew point in celsisus
bme280_math.qfe2qnh()¶
For given altitude converts the air pressure to sea level air pressure (QNH).
Syntax¶
bme280_math.qfe2qnh([self], P, altitude)
Parameters¶
- (optional)
self
userdata or table structure so that the function can be directly called as object method, parameter is ignored in the calculation P
measured pressurealtitude
altitude in meters of measurement point
Returns¶
sea level pressure
bme280_math.read()¶
Reads the sensor and returns the temperature, the air pressure, the air relative humidity and see level air pressure when altitude
is specified.
Syntax¶
bme280_math.read(bme280sensor, registers, [altitude])
Parameters¶
bme280sensor
- BME280 sensor user data returned bybme280_math.setup()
registers
- string of 8 bytes (chars) registers read fromBME280_REGISTER_PRESS
- (optional)
altitude
- altitude in meters of measurement point. If provided also the air pressure converted to sea level air pressure is returned.
Returns¶
T
temperature in celsiusP
air pressure in hectopascalsH
relative humidity in percent- (optional)
QNH
air pressure in hectopascals
Returns nil
if the conversion is not successful.
bme280_math.setup()¶
Initializes module. Initialization is mandatory before read values.
Syntax¶
bme280_math.setup(registers, [temp_oss, press_oss, humi_oss, power_mode, inactive_duration, IIR_filter])
Parameters¶
- registers - String of configuration registers read from the BME280 sensor. It consists of 6 bytes (chars) of
BME280_REGISTER_DIG_T
, 18 bytes (chars)BME280_REGISTER_DIG_P
and optional (not present for BMP280 sensor) 8 bytes (chars) ofBME280_REGISTER_DIG_H1
(1 byte) andBME280_REGISTER_DIG_H2
(7 bytes) - (optional)
temp_oss
- Controls oversampling of temperature data. Default oversampling is 16x. - (optional)
press_oss
- Controls oversampling of pressure data. Default oversampling is 16x. - (optional)
humi_oss
- Controls oversampling of humidity data. Default oversampling is 16x - (optional)
sensor_mode
- Controls the sensor mode of the device. Default sensor more is normal. - (optional)
inactive_duration
- Controls inactive duration in normal mode. Default inactive duration is 20ms. - (optional)
IIR_filter
- Controls the time constant of the IIR filter. Default filter coefficient is 16.
temp_oss , press_oss , humi_oss |
Data oversampling |
---|---|
0 | Skipped (output set to 0x80000) |
1 | oversampling ×1 |
2 | oversampling ×2 |
3 | oversampling ×4 |
4 | oversampling ×8 |
5 | oversampling ×16 |
sensor_mode |
Sensor mode |
---|---|
0 | Sleep mode |
1 and 2 | Forced mode |
3 | Normal mode |
Using forced mode is recommended for applications which require low sampling rate or hostbased synchronization. The sensor enters into sleep mode after a forced readout. Please refer to BME280 Final Datasheet for more details.
inactive_duration |
t standby (ms) |
---|---|
0 | 0.5 |
1 | 62.5 |
2 | 125 |
3 | 250 |
4 | 500 |
5 | 1000 |
6 | 10 |
7 | 20 |
IIR_filter |
Filter coefficient |
---|---|
0 | Filter off |
1 | 2 |
2 | 4 |
3 | 8 |
4 | 16 |
Returns¶
bme280sensor
user data (nil
if initialization has failed)config
3 (2 for BME280) field table with configuration parameters to be written to registersBME280_REGISTER_CONFIG
,BME280_REGISTER_CONTROL_HUM
,BME280_REGISTER_CONTROL
consecutively
Example¶
See bme280 Lua module documentation.
BME280 (selected) registers¶
name | address |
---|---|
BME280_REGISTER_CONTROL | 0xF4 |
BME280_REGISTER_CONTROL_HUM | 0xF2 |
BME280_REGISTER_CONFIG | 0xF5 |
BME280_REGISTER_CHIPID | 0xD0 |
BME280_REGISTER_DIG_T | 0x88 (0x88-0x8D (6)) |
BME280_REGISTER_DIG_P | 0x8E (0x8E-0x9F (18)) |
BME280_REGISTER_DIG_H1 | 0xA1 |
BME280_REGISTER_DIG_H2 | 0xE1 (0xE1-0xE7 (7)) |
BME280_REGISTER_PRESS | 0xF7 (0xF7-0xF9 (8)) |